Welcome to the Nanoscale Materials Lab
The Nanoscale Materials Laboratory, established through an agreement between the Department of Physics of the University of Trieste (Department of Excellence 2023-2027) and Elettra, brings together researchers and students investigating Surfaces, 2D Materials and Atomic Clusters Physics, in close collaboration with Elettra scientists. Among its facilities, the nmLAB hosts the size-selected nanocluster source ENAC (Exact Number of Atoms in each Cluster). The nmLAB is part of the National Quantum Science and Technology Institute, funded through the PNRR. Since 2000, more than 100 students have carried out experimental research in the lab for their Master's degree in Physics and within the PhD in Nanotechnology and Physics programmes. The Lab also hosts the Training Activity of the Laboratory of Nanomaterials Physics course for undergraduate Physics students at UniTS.
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From clusters to atoms: spontaneous fragmentation of metal nanoclusters on magnetite
Size-selected clusters can lose their identity upon soft landing, as strong interactions with magnetite drive their spontaneous fragmentation.
G. Coltrioli, D. Perco et al.,
J. Am. Chem. Soc. 148, 41612 (2026)
Below 1 nm, the properties of matter are exquisitely sensitive to the exact number and arrangement of atoms. This has made size-selected clusters particularly attractive as model systems for understanding how catalytic and functional properties emerge between the atomic and bulk limits. However, this approach implicitly assumes that a cluster reaching a surface preserves, at least to some extent, the atomic identity that was so carefully selected before deposition. Our work shows that this assumption can fail completely.
We investigate the deposition of extremely small, mass-selected early-transition-metal clusters onto a well-defined magnetite surface, Fe₃O₄(001).
Because the clusters are selected in the gas phase according to their exact mass, the number of metal atoms reaching the surface is precisely known.
Their evolution after soft landing is followed by combining high-resolution photoelectron spectroscopy with scanning probe microscopy and first-principles calculations.
Rather unexpectedly, the deposited clusters do not necessarily remain intact.
For specific cluster sizes and compositions, the interaction with magnetite is sufficiently strong to induc spontaneous fragmentation already at room temperature.
The surface therefore does much more than simply immobilize the incoming clusters: it actively reshapes them and can ultimately destroy their original structure.
The driving force originates from the strong interaction between the early transition-metal atoms and the oxygen atoms of the oxide surface.
Formation of new metal–oxygen bonds can compensate, or even overcompensate, the energetic cost required to break the metal–metal bonds within the cluster.
As a consequence, fragmentation becomes energetically favorable without requiring high-temperature activation.
The process produces highly dispersed surface species and, under appropriate conditions, even isolated metal atoms derived directly from the fragmentation of the deposited clusters.
This observation changes the conventional picture of cluster deposition.
The relevant nanoscale object is no longer necessarily the cluster that was produced and mass-selected before deposition, but rather the structure resulting from the competition between intracluster cohesion and cluster–surface interaction.
Magnetite plays a particularly important role in this balance because its surface provides chemically active oxygen sites capable of forming strong bonds with the deposited metal atoms.
The calculations reveal how this interaction modifies both the geometry and electronic structure of the incoming clusters and identifies the energetic pathway leading from an intact cluster to dispersed surface species.
The experiments provide direct spectroscopic evidence that the chemical environment of the deposited atoms changes profoundly upon interaction with the oxide.
Together, experiment and theory therefore establish a microscopic picture in which cluster fragmentation is an intrinsic consequence of the energetics of the supported system rather than an accidental effect of deposition.
The result also has important implications for single-atom catalysis.
Isolated atoms on oxide surfaces are commonly prepared by depositing individual atoms or by exploiting specific trapping sites that prevent their aggregation.
Our results demonstrate a conceptually different pathway: single atoms can emerge spontaneously from larger, precisely defined clusters through support-induced fragmentation.
This suggests that the formation of atomically dispersed species may in some cases be governed by processes occurring immediately upon cluster–support contact.
More generally, our findings emphasize that the properties of supported nanoclusters cannot be understood by considering the free cluster and the substrate as two essentially independent components.
At the sub-nanometric scale, the interaction with the support can become comparable to, or stronger than, the forces holding the cluster itself together.
The surface can therefore determine not only where a cluster binds and what its electronic structure becomes, but even whether the cluster continues to exist as a cluster at all.
This provides a broader perspective for designing supported nanomaterials: controlling cluster size before deposition is only the first step; understanding whether that size and structure survive contact with the support is equally fundamental.
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Room-Temperature Adsorption on Magnetite Induces Spontaneous Fragmentation of Early Transition-Metal Size-Selected Nanoclusters
Gabriele Coltrioli, Deborah Perco, Luca Sementa, Marco Bianchi, Ancrea Berti, Mikhail Bandurist, Paolo Lacovig, Silvano Lizzit, Aras Kartouzian, Ueli Heiz, Alessandro Fortunelli, and Alessandro Baraldi
J. Am. Chem. Soc. 148, 41612 (2026)
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When cooling does not freeze the structure: nanocluster fluxionality at low temperature
Even at temperatures where structural dynamics are expected to be largely suppressed, nanoclusters retain a remarkable ability to rearrange.
Y. Wei, D. Perco et al.,
ACS Nano 20, 25203 (2026)
At the sub-nanometric scale, matter can behave in ways that have no direct counterpart in bulk materials. One of the most intriguing manifestations of this behavior is fluxionality, i.e., the ability of a cluster to explore different atomic configurations in response to relatively small energetic perturbations. Such structural flexibility is increasingly recognized as a key ingredient in the chemical properties of nanoclusters, particularly in catalysis. Yet, one would naturally expect this dynamic behavior to become strongly suppressed at very low temperature, where thermal energy is insufficient to overcome the barriers separating different configurations.
Our work shows that this intuitive picture can break down dramatically for size-selected molybdenum nanoclusters supported on graphene.
We investigate clusters containing only a few Mo atoms, up to Mo₁₃, deposited on epitaxial graphene and exposed to molecular oxygen at temperatures as low as 40 K. Their oxidation is followed experimentally by high resolution X-ray photoelectron spectroscopy (HR-XPS) and interpreted through extensive first-principles calculations of the complete supported systems.
At such low temperature, conventional thermally activated restructuring would be expected to be strongly inhibited. Nevertheless, the clusters undergo profound structural transformations as their interaction with oxygen proceeds.
The key to this unexpected behavior is the coupling between oxygen dissociation, electronic excitation, and the exceptionally soft structural energy landscape of the clusters.
The interaction with oxygen does not simply decorate an essentially rigid metallic nanoparticle. Instead, increasing oxygen incorporation progressively reorganizes the entire cluster, producing substantial changes in Mo–Mo distances, coordination, and overall cluster geometry.
This structural flexibility allows the clusters to accommodate extraordinarily large amounts of oxygen. Oxygen contents far exceeding those expected from the stoichiometry of stable bulk molybdenum oxides can be reached, demonstrating that bulk stoichiometric rules cease to provide an adequate description at the sub-nanometric limit.
The calculations reveal that oxygen incorporation progressively expands and restructures the clusters and promotes local coordination environments that do not have a simple bulk counterpart. In particular, highly oxygenated configurations contain MoO₄-like tetrahedral motifs, which provide an efficient way of stabilizing oxygen-rich structures.
An important consequence is that the conventional assignment of a unique formal oxidation state to each Mo atom becomes increasingly inadequate. The measured Mo 3d core-level shifts are better understood in terms of the continuously evolving local atomic valence and coordination environment, together with final-state screening effects.
The remarkable aspect of these observations is their occurrence at temperatures at which the available thermal energy alone should be far too small to sustain extensive structural rearrangements.
The energy released or transferred during oxygen activation provides access to otherwise inaccessible regions of the potential-energy landscape. The cluster can therefore reorganize while the chemical process is occurring, rather than having to overcome the relevant barriers through thermal activation alone.
Fluxionality in these systems should consequently not be regarded simply as the thermal motion of a small particle between nearly degenerate structures. Instead, the chemical reaction itself can activate the structural degrees of freedom of the cluster.The resulting picture is therefore one of a strongly coupled process: oxygen activation modifies the electronic structure, the cluster responds structurally, and this structural response in turn enables additional oxygen incorporation and stabilization.
Our results demonstrate that even at cryogenic temperatures, sub-nanometric clusters cannot necessarily be described as static atomic structures.
They are better viewed as adaptive nanoscale entities whose structure evolves together with their chemical environment.
This behavior has important implications for understanding heterogeneous catalysis and other chemical processes involving clusters containing only a few atoms. The structure responsible for reactivity may not correspond to the initially deposited cluster, nor even to a single well-defined equilibrium geometry.
More generally, the results illustrate how reducing matter to the sub-nanometric scale can fundamentally alter the relationship between temperature, structure, stoichiometry, and chemical reactivity.
In this regime, cooling does not necessarily freeze the structure: chemical energy can keep the atomic landscape accessible even when thermal energy cannot.
Retrieve article
Photon-Driven Cluster Fluxionality: Breaking the Bulk Stoichiometry Ceiling in Subnanometric Molybdenum Oxides
Yao Wei, Deborah Perco, Alejandro Santana-Bonilla, Fderico Loi, Paolo Lacovig, Silvano Lizzit, Lev Kantorovich, Alessandro Baraldi
ACS Nano 20, 25203 (2026)
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Coexisting 1D and 2D wave patterns in graphene
Highly anisotropic substrate induces coesixtence of double corrugation in epitaxial graphene.
D. Perco et al., Carbon 147, 215012 (2025)
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Ultra-fast atomic diffusion on graphene
Ultra-low atomic diffusion barrier of Pt atoms on graphene was determined by combining High-Resolution XPS and DFT
A. Berti et al., ACS Nano 19, 35921 (2025)
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Challanges in the oxidation at the sub-nanoscale
At the sub-nanometric scale, determining oxidation states becomes increasingly complex, as the properties of matter are strongly influenced by the discrete number of atoms involved.
D. Perco et al., J. Am. Chem. Soc. 147, 215012 (2025)
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Oxygen on the top of the smallest mountain
Due to the corrugation of graphene and the electronic structure of matter on the sub-nanometer scale, oxygen only adsorbs on top of very small size-selected Pt clusters
F. Loi et al., Small Structures 2400250, (2024)
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